Correlators with one-digit digital sampling are known. Their use has become important, particularly in communication engineering and measuring techniques. Their use has also become important in all those instances in which, in the broadest sense, a wave-like signal has to be compared to another wave-like signal.
When, for example, the signal sequence with hard limitation of an emitted sound signal is correlated with one of the echo, it is possible to determine the traveled distance of the sound waves to their reflection from the shift period of the two signal sequences. Also belonging to the state of the art are related uses such as for an adjusted filter, for signal recognition and for pattern recognition.
From the German Auslegeschrift No. 26 49 081, there has become known a distance measurement device in which echo signals to be evaluated are processed by using correlation techniques.
The correlator used in this case is taken from the U.S. Pat. No. 3,786,405 and consists essentially of components which are also described in the German Auslegeschrift No. 2 204 028. These components are, first, a sampling unit which samples the signal delivered from a limiter with relatively high sampling speed, and a switch (gate circuit) which introduces the signals waiting in the line from the sampling unit to a first or second time-compression circuit. Each time-compression circuit has a two-position switch which, in dependence on the signal of a time control device, either connects a subsequent shift register to the sampling unit for writing in a signal, or sets the output line of the register to its input so that the bits emerging from the register are pushed around in a circle.
Moreover, the output of the register is connected to a coincidence detector which generates a logically high signal, in the case of consistency of bits, or a logically low signal, in the case of inconsistency, and delivers the signal to an integrator.
An essential property of this correlator is that one shift register is shorter by one bit than the other, so that the circulating signal sequences are shifted relative to each other by one bit in each circulation.
Correlators of the above-described kind have, on the one hand, registers of fixed length. Accordingly, an adjustment to different signal sequences is only possible when different correlators are used. On the other hand, certain portions cannot merely be selected from the register and correlated since, under all conditions, only the entire content can be analyzed. In addition, the shift period of these registers is preselected in a fixed manner so that they have a relatively low operational mobility. With the known correlators, it is not possible to carry out a multi-dimensional correlation in an economically sensible manner.